Radio receiving set



Dec. 28 1926.

W. K. THOMAS RADIO RECEIVING SET Filed Sept. 12. 1922 MN L Patented Dec. 28, 1926.

. UNITED STATS PATENT OFFICE.

WILLIAM K. THOMAS, OF GRAFTON, BENNSYLVANIA, ASSIGNOR TO SAMUEL A.

IPIGKEBING, OF PITTSBURGH, PENNSYLVANIA.

RADIO RECEIVING sEr.

Application filed September This invention relates to radio receiving sets, and moreparticularly to those sets embodying audlon bulbs.

Heretofore, a great objection to the use of tent, especially where several stages of amplification are used.

lVhile this noise and humming has been attributed to various sources, I have found that a large part of it is due to the fact that radio-frequency waves are not the only ones received by an audion set. treet-car noises and numerous other low-frequency noises are also received.

The ordinary audion set rectifies or detects incoming messages immediately. That is, the first bulb of the set not only rectifies the waves but also reduces them from a radio-frequency to a comparatively low audio-frequency. This arrangement al.- lows the low-frequency waves which are received to pass on with the desired signals, and as a result humming and interference is set up, the effect of which is greatly magnified by every amplification.

I have found by experiment that by modifying the usual connections in an audion set it is possible to amplify the incoming waves at radio-frequency before they are rectified or detected. By so doing, I effectually eliminate all low-frequency waves which may have made their way into the set, and when rectification is effected only the radiofrequency waves pass on. V

The damping out of low-frequency waves before rectification results in much clearer messages than are generally attainable. The set is also less sensitive to small outside influences which are generally bothersome on audion sets, and much of the shielding of sets by copper sheets and various other de vices may be done away with. The set 1s also easier to tune, since there are no extraneous low-frequency sounds to be damped out, a problem which has heretofore required very close and delicate tuning.

The accompanying drawing is a diagrammatic showing of the preferred form of my invention.

In the illustrated embodiment of the invention, the antenna circuit comprises an 12, 1922. Serial No. 587,729.

antenna 1 connected to a coil 2. The coil 2 is provided with a plurality of taps 3. By means of a switch 4 connected to the ground, the efiective length of the coil may be varied by switching to any of the taps as may be necessary for tuning.

The oscillations in the antenna circuit set up a corresponding oscillation in a secondary winding 5. The windings 2 and 5 form a loose-coupled connection. They are illustrated as being the two windings of a variocoupler.

One end of the winding 5 terminates in the grid 6 of an audion bulb 6. A wire 7 from the other end of the winding is con nected to the positive terminal of a battery 8, whose potential is preferably about 6 volts. Connected to the wire 7 is a wire 9 terminating in the positive filament terminal of the audion 6. The negative terminal of the filament 6 is connected to a filament rheostat 10 and back to the negative terminal of the battery 8 Shunted across the secondary winding 5 is a variable condenser 11. One side of the condenser is connected directly to the secondary winding 5, but the other is connected in series with the filament 6 of the audion 6 and with a small resistance. This resistance may be a portion of the filament resistance 10, and I have found by experiment that about 1 ohm is required for best results. The variable condenser when so connected is of great value in tuning the set and assists in giving clear and sharp signals.

The plate 6 of the bulb 6 is connected to the primary winding of an air cored transformer 12. The other end of the primary winding is connected to the positive terminal of the battery 13, whose potential is preferably about volts. I have found that good results are obtained by using a transformer with windings in the ratio of about 130/165 turns.

One terminal of the secondary winding of the transformer .12 is connected to the grid 14 of a second audion 14. Between the secondary and the grid is a grid condenser 15 and a grid lead 16 which may be five tenthousandths microfarads and two megohms, respectively. The other terminal of the secondary, instead of making the usual connection with the negative terminal of the filament 14 of the audion 14, is connected through a small resistance. For this purpose I use a small portion of the filament rheostat 17. The grid is therefore given a different potential, in this case negative, with respect to the filament, or biased with respect to the filament. This biasing of the grid materially increases the sensitiveness of the audion. The audion may be adjusted to a very sensitive condition by adjusting the biasing by means of adjusting at the amount of the resistance of the filament rheostat 17 used for this purpose. hen the grid is given a negative potential, or bias, with respect to the filament, it tends to decrease the electronic discharge from the '3 filament to the plate, but when biased positively, it tends to increase such electronic discharge. lVhile in some cases I may desire to bias the grid positively with respect to the filament, I have found that in most cases it 1 is desirable to give it a negative bias, as

shown. I provide a similar bias for the grid 18 of the audion 18, which amplifies at au- Clio-frequency.

Different numbers of audion bulbs may be 1': employed for amplifying the radiofrequenthe plate 18 of the audion 18. The telephones 19 are connected to the audion 18 and battery 13 in the usual manner.

Experiments have amply shown the practicability and effectiveness of the apparatus. The various features, such as the connection of the variable condenser across the second ary winding of the vario-coupler in series with the filament and a portion of the filament rheostat, the biasing of the audion grids, and the amplification of radio-frequency before rectification, all combine to make an extremely efiicient and sensitive receiving set.

ll hile I have described one embodiment of my invention, it will be understood that this does not define the limits of my invention, as changes may be made in the construction and operation within the scope of the following claim.

I claim:

In a high frequency amplifying circuit, an air core transformer, a tuning condenser and a filament lighting battery, one plate of the condenser being connected to one end of the transformer secondary and to the grid of a vacuum tube, the other plate of the condenser being connected to the negative pole of the battery, and the other end of the transformer secondary being connected to the positive pole of said battery, whereby a positive potential is placed on the grid, and said battery is placed in series with the coil and condenser.

In testimony whereof I have hereunto set my hand.

WILLIAM K. THOMAS. 

